[Feature Flags] Support semantic version operators

[greghuels]

Summary of changes

Adds support for the SEMVER_EQ, SEMVER_NEQ, SEMVER_LT, SEMVER_LTE, SEMVER_GT, and SEMVER_GTE Feature Flags condition operators.

Syncs the canonical semver flag configuration and all 13 evaluation cases from DataDog/ffe-system-test-data#20 into the bundled fixture suite.

Reason for change

Feature Flags targeting rules need semantic version comparisons that behave consistently across SDKs. This brings the .NET evaluator in line with the Go implementation and the shared FFE system-test data.

Implementation details

• Adds a strict semantic version parser and comparer with prerelease precedence and build-metadata total ordering.
• Treats invalid, missing, or non-string semver operands as non-matches.
• Routes all six semver operators through the new comparer.
• Updates the bundled fixture runner to assert canonical evaluation reasons and treat omitted variants as unspecified.

Test coverage

• Ports all 27 table-driven semver evaluator cases from feat(openfeature): support semantic version conditions dd-trace-go#5128 one-for-one.
• Covers the Go tests for missing attributes and unsupported operators.
• Canonical bundled fixtures: 224 passed, including all 13 semver evaluation rows.
• Complete Feature Flags test namespace: 389 passed.
• Includes focused parser, ordering, invalid-syntax, and operator-deserialization coverage.
• Verified net461 and netstandard2.0 production builds.
• Verified whitespace formatting and git diff --check.

Other details

• Internal ticket: FFL-2919
• Go reference: feat(openfeature): support semantic version conditions dd-trace-go#5128
• Shared fixture reference: Add SEMVER comparison operator fixtures ffe-system-test-data#20

[greghuels]

Closing this out since there have been some changes in the Go SDK and rewriting this from scratch will be safer and easier